An internal combustion engine may be used as a motor vehicle drive unit. Within the context of the present disclosure, an internal combustion engine may encompass an Otto-cycle engines but also diesel engines and hybrid internal combustion engines, which utilize a hybrid combustion process, and also hybrid drives which comprise not only the internal combustion engine but also an electric machine which can be connected in terms of drive to the internal combustion engine and which receives power from the internal combustion engine or which, as an activatable auxiliary drive, additionally outputs power.
In the development of internal combustion engines, it may be desired to decrease fuel consumption to increase efficiency. Fuel consumption and thus efficiency may pose a problem. The reason for this lies in the fundamental operating process of the Otto-cycle engine. Load control may be carried out via a throttle flap arranged in the intake system. By adjusting the throttle flap, the pressure of the inducted air downstream of the throttle flap can be adjusted. The further the throttle flap is closed, that is to say the more said throttle flap blocks the intake system, the higher the pressure loss of the inducted air across the throttle flap, and the lower the pressure of the inducted air downstream of the throttle flap and upstream of the inlet into the at least two cylinders, that is to say combustion chambers. For a constant combustion chamber volume, it is possible in this way for the air mass, that is to say the quantity, to be set based on the pressure of the inducted air. Thus, quantity regulation may be undesired, specifically in part-load operation, because low loads demand a high degree of throttling and a large pressure reduction in the intake system, as a result of which the charge exchange losses increase with decreasing load and increasing throttling.
One approach to a solution for dethrottling the Otto-cycle engine is for example an Otto-cycle engine operating process with direct injection. The direct injection of the fuel may realize a stratified combustion chamber charge. The direct injection of the fuel into the combustion chamber may permit regulation in the Otto-cycle engine, within certain limits. The mixture formation takes place by the direct injection of the fuel into the cylinders or into the air situated in the cylinders, and not by external mixture formation, in which the fuel is introduced into the inducted air in the intake system. However, fuel/air mixing may not sufficiently mix at all engine operating conditions.
Another approach to a solution for dethrottling the Otto-cycle engine comprise in the use of an at least partially variable valve drive. By contrast to invariable valve drives, in which both the lift of the valves and the control timing are invariable, these parameters which have an influence on the combustion process, and thus on fuel consumption, can be varied to a greater or lesser extent via variable valve drives. If the closing time of the inlet valve and the inlet valve lift can be varied, then throttling-free and thus loss-free load control may be possible. The mixture mass which flows into the combustion chamber during the intake process is then controlled via a throttle flap but rather via the inlet valve lift and the opening duration of the inlet valve. Variable valve drives may be expensive and are therefore often undesired for mass production.
A further approach to a solution for dethrottling the Otto-cycle engine may include cylinder deactivation, that is to say the deactivation of individual cylinders in certain load ranges. The efficiency of the Otto-cycle engine in part-load operation may be improved, that is to say increased, via partial deactivation of at least one cylinder of a multi-cylinder internal combustion engine which may increase the load on the other cylinders, which remain in operation, if the engine power remains constant, such that the throttle flap may be opened further to introduce a greater air mass into operating cylinders, whereby dethrottling of the internal combustion engine is attained overall. During the partial deactivation, the cylinders which are permanently operational (e.g., may not be deactivated) operate in the region of higher loads, at which the specific fuel consumption is lower. The load collective of the operational cylinders is shifted toward higher loads.
The operating (e.g., combusting) cylinders during the partial deactivation furthermore exhibit increased air/fuel mixing owing to the greater air mass or mixture mass supplied, and tolerate higher exhaust-gas recirculation rates. Furthermore, the deactivated (e.g., non-combusting) cylinder increases in efficiency, as heat losses due to heat transfer between combustion gases and combustion chamber walls are reduced and/or eliminated.
It will be appreciated that diesel engines may experience similar benefits from cylinder deactivation. More specifically, the partial deactivation may at least partially prevent a diesel fuel-air mixture from becoming too lean in the context of the quality regulation in the presence of decreasing load as a result of a reduction of the fuel quantity used.
However, the inventors herein have recognized potential issues with such systems. As one example, pumping losses may occur in the deactivated cylinders, which may decrease an overall power output of the engine, thereby decreasing overall fuel efficiency. Said another way, the deactivated cylinders continue to participate in a charge exchange, wherein the deactivated cylinders continue to compress intake air. As described above, these pumping losses may be remedied via switchable valve drive, such as a variable valve drive. However, these solutions are expensive and demand complex electrical connections which are prone to degradation.
To decrease the cost, it may be desired for switchable or adjustable valve drives to be arranged at the inlet side and at the outlet side, where valve drives of the deactivated cylinders are held closed, and thus no longer participate in the charge exchange, during the partial deactivation. In this way, a situation is also prevented in which the relatively cool charge air conducted through the deactivated cylinders reduces the enthalpy of the exhaust-gas flow provided to the turbine and causes the deactivated cylinders to rapidly cool down.
Furthermore, in the case of internal combustion engines supercharged via exhaust-gas turbocharging, switchable valve drives can lead to further problems because the turbine of an exhaust-gas turbocharger is configured for a certain exhaust-gas flow rate above a threshold, and thus generally also for a certain number of cylinders. If the valve drive of a deactivated cylinder is deactivated, the total mass flow through the cylinders of the internal combustion engine is initially reduced. The exhaust-gas mass flow conducted through the turbine decreases, and the turbine pressure ratio generally also decreases as a result. A decreasing turbine pressure ratio has the effect that the charge pressure ratio likewise decreases, that is to say the charge pressure falls, and less charge air is or can be supplied to the cylinders that remain operational.
It may be desired for the charge pressure to be increased to supply more charge air to the cylinders that remain operational, because in the event of deactivation of at least one cylinder of a multi-cylinder internal combustion engine, the load on the other cylinders, which remain operational, increases, for which reason a greater amount of charge air and a greater amount of fuel may be supplied to said cylinders. The drive power available at the compressor for generating an adequately high charge pressure is dependent on the exhaust-gas enthalpy of the hot exhaust gases, which may determined by the exhaust-gas pressure and the exhaust-gas temperature, and the exhaust-gas mass or the exhaust-gas flow.
By opening the throttle flap, the charge pressure may be increased in the load range relevant for partial deactivation. This possibility may not exist in the case of the diesel engine. The small charge-air flow may have the effect that the compressor operates beyond the surge limit.
The effects described above may lead to a restriction of the practicability of the partial deactivation, specifically to a restriction of the engine speed range and of the load range in which the partial deactivation can be used. In the case of low charge-air flow rates, it may not be desired owing to inadequate compressor power or turbine power, for the charge pressure to be increased in accordance with demand.
The charge pressure during partial deactivation, and thus the charge-air flow rate supplied to the cylinders that remain operational, may for example be increased via a small configuration of the turbine cross section and via simultaneous exhaust-gas blow-off, whereby the load range relevant for a partial deactivation may also be expanded again. However, the supercharging behavior may be inadequate when all the cylinders are operated, which may decrease power output and/or fuel economy.
The charge pressure during partial deactivation, and thus the charge-air flow rate supplied to the cylinders that are still operational, may also be increased by virtue of the turbine being equipped with a variable turbine geometry, which permits an adaptation of the effective turbine cross section to the present exhaust-gas mass flow. The exhaust-gas back pressure in the exhaust-gas discharge system upstream of the turbine would then however simultaneously increase, leading in turn to higher charge-exchange losses in the cylinders that are still operational.
In the internal combustion engine according to the present disclosure, the cylinders of a second group (e.g., inner cylinders) are not equipped with deactivatable valve drives either at the inlet side or at the outlet side. Rather, the deactivated cylinders continue to participate in the charge exchange, that is to say the valves oscillate, during the partial deactivation. The internal combustion engine to which the present disclosure relates however may comprise at least one shut-off element at the inlet side and at the outlet side to optionally prevent the supply of fresh air to the deactivated cylinders and the discharge of exhaust gas from the deactivated cylinders. During the partial deactivation, the piston of a deactivated cylinder draws gas in via the at least one inlet opening and forces gas out via the at least one outlet opening. The gas is however enclosed, that is to say trapped, between the shut-off element arranged at the inlet side and the shut-off element arranged at the outlet side. This may solve the charge losses incurred and/or accepted in the previous examples described above.
In one example, the issues described above may be addressed by an internal combustion engine comprising at least one cylinder head with at least two cylinders, in which each cylinder of the two cylinders has at least one inlet opening fluidly coupled to an intake line for the supply of fresh air via an intake system, each cylinder has at least one outlet opening fluidly coupled to an exhaust line for the discharge of the exhaust gases via an exhaust-gas discharge system, the at least two cylinders form a first cylinder group and a second cylinder group, the first cylinder group comprising at least a first cylinder and the second cylinder group comprising at least a second cylinder different than the first, where the first cylinder is not switchable and the second cylinder is switchable, the intake system comprising a primary shut-off element configured to adjust fresh air flow to each of the first and second cylinder groups and a secondary shut-off element configured to adjust fresh air flow to only the second cylinder group, via which the supply of fresh air to the at least one cylinder of the second group can be stopped, a second cylinder group exhaust line is equipped with at least one exhaust shut-off element configured to adjust exhaust gas flow from the second cylinder group exhaust line to the exhaust-gas discharge system, and a negative-pressure source fluidly coupled to at least the second cylinder group exhaust line, where a negative-pressure line fluidly coupling the negative pressure source is connected to the second cylinder group exhaust line at a position between the exhaust shut-off element and the second cylinder. In this way, the gas of a deactivated cylinder that has been enclosed or trapped between the at least one shut-off element of the intake system of the second group and the at least one shut-off element of the exhaust-gas discharge system of the second group during partial deactivation is at least partially extracted by suction, that is to say evacuated or discharged, via a negative-pressure line.
As one example, the gases situated in a cylinder that is deactivated during the partial deactivation poses less resistance to the oscillating piston of the deactivated cylinder during the intake, exhaust and compression. In this way, the charge-exchange losses of the second cylinder group during partial deactivation may be reduced and fuel economy may be increased. The at least one negative-pressure line of the internal combustion engine according to the disclosure branches off between the at least one shut-off element of the intake system of the second group and the at least one shut-off element of the exhaust-gas discharge system of the second group, and is connectable or connected to a negative-pressure source, for example a vacuum pump. A shut-off element associated with the line serves for opening up and closing off the negative-pressure line.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.